Questionable expression of unstable DQ heterodimer containing HLA‐DQA1*01:07

Abstract

Human leukocyte antigens (HLA)‐DQA1*01:07 was identified as an HLA‐DQ blank specificity that segregated with the serological HLA‐A2, ‐B7, ‐DR14, ‐DR52 haplotype, which carried DQB1*05:03. The blank specificity of DQA1*01:07‐DQB1*05:03 may be because of lack of reactivity of available typing sera, or disruption of proper assembly of DQ heterodimer. The cDNA sequence of DQA1*01:07 is nearly identical to DQA1*01:04 except for a variant at position 304, which results in the replacement of an arginine with a cysteine at 79α. To determine whether the DQA1*01:07 product can be expressed on cell‐surface, we co‐expressed DQA1*01:07 with various DQB1*05 or *06 alleles in fibroblast cells. Cell‐surface expression of DQ was detectable when DQA1*01:07 was co‐expressed with DQB1*06:04 but undetectable with other DQB1*05 and DQB1*06 alleles, including DQB1*05:03, to which DQA1*01:07 was encoded in cis. These data suggest that DQA1*01:07 may act as a phenotypically null allele in the DQA1*01:07‐DQB1*05:03 haplotype, while it can be expressed at a low level in the presences of certain DQB1*06 alleles, such as DQB1*06:04, in trans. Based on the null or low expression of DQA1*01:07 as shown in the previous and present studies, DQA1*01:07 has recently been renamed to DQA1*01:07Q, indicating its questionable expression.